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PT/INR (Prothrombin Time) Test
✅ Up to date🔬 Evidence: ModerateHematology
Diğer adları: International normalized ratio, Prothrombin time, Pro time
⚠️
Discuss your test results with your doctor. This page is for informational purposes only and does not provide a diagnosis.
⚡ Key Facts
• PT measures clotting time in seconds via the extrinsic and common pathways
• INR standardizes PT results for warfarin monitoring
• Therapeutic INR for most indications: 2.0–3.0
• Also reflects liver synthetic function
🧪 What Does This Test Measure?
The PT/INR test measures how long it takes blood to clot through the extrinsic pathway, with INR standardizing results across laboratories for warfarin monitoring.
📋 Why Is It Ordered?
Ordered for warfarin therapy monitoring, liver synthetic capacity evaluation, preoperative bleeding risk assessment, and vitamin K deficiency investigation.
🔧 Preparation
Fasting is generally not required. Blood is collected in a citrated tube. Consistent vitamin K intake is important for warfarin patients.
📊 Reference Ranges
PT: approximately 10–13.5 seconds (varies by laboratory)
INR (not on anticoagulants): approximately 0.8–1.1
INR (warfarin therapy): typically 2.0–3.0
⚠️ Ranges vary by laboratory and reagent.
⬆️ High Values
Prolonged PT or elevated INR may be associated with warfarin use, liver disease, vitamin K deficiency, DIC, or factor deficiencies.
⬇️ Low Values
Shortened PT or low INR is rarely evaluated clinically. It generally indicates adequate or enhanced clotting function.
⚙️ What Can Affect Results?
Medications, vitamin K intake, liver function, laboratory method, and sample quality may affect PT/INR results.
🔬 Evidence Summary
Moderate evidence: 5 guidelines and 2 reviews.
✅ Key Takeaways
💡
What you learned: PT measures clotting time; INR standardizes it for warfarin monitoring. Prolonged PT may also indicate liver disease or vitamin K deficiency.
⛔
A PT/INR result alone cannot determine bleeding risk. Clinical context and medication history are essential.
🔬 Sources Used on This Page
7 sources · Most recent publication: 2026📋
Guideline
Expert society and guideline recommendations
5
sources
📖
Review
Comprehensive topic evaluation
2
sources
Overall assessment: Evidence level for this topic is moderate. This page is supported by 5 guidelines, 2 reviews.
📝 Questions to Ask Your Doctor
Be prepared for your appointment. Add questions to your list.
Last reviewed: 4/2/2026
Next review: 7/2/2026
⚖️ Comparisons
🔗 Related Topics
🧪 D-dimer🧪 aPTT (aktive parsiyel tromboplastin zamanı)🧪 Fibrinojen🧪 Hemogram (trombosit sayısı)🧪 ALT/AST (karaciğer enzimleri)
⚖️ This page does not replace medical advice. Make treatment decisions with your doctor.
Content is based on scientific studies indexed in PubMed and current clinical guidelines.
Content is based on scientific studies indexed in PubMed and current clinical guidelines.